A special-duty bridge-laying vehicle is known that is used to transport the bridge sections to the location where the bridge is to be laid, to position the bridge sections as they are assembled together, and to subsequently pull or pick up the bridge so it can be used elsewhere. Such a vehicle, which is typically tracked but which can have standard highway wheels, is provided with a laying arm that serves several functions. First of all it handles and positions the bridge sections, positioning them on the river bank or picking them up off the bank or other declivity that must be bridged. It also holds the bridge sections as they are joined together and allows the assembled bridge to be thrust across the river or other declivity while compensating for uneven ground conditions.
One known bridge-laying apparatus described in German patent document 2,403,494 has a laying arm moved either by a central longitudinally effective hydraulic cylinder or by two right and left-hand parallel-working cylinders. Since the laying arm pivots about an axis on the laying-vehicle frame, with every movement the bridge section being handled is moved longitudinally. This makes it very hard to get the sections aligned with each other for proper assembly while making positioning the finished structure on the terrain also fairly difficult. In addition any movement of the laying arm entails a tipping action that once again makes it difficult to align the various parts.
German published patent application 4,127,106 of Karcher describes another system wherein the laying arm is mounted at the rear end via a lever arm to the vehicle frame and in the transport or starting position its middle part is secured removably on an axis fixed to the vehicle while in the laying position it is mounted via a joint to an extensible leg that stands on the ground. A hydraulic cylinder is linked to the lever arm to lift and lower it simultaneously with the rear end of the laying arm. If either the middle part of the laying arm is resting on the axis fixed to the vehicle frame or the front part on the extensible leg, the laying arm extends at different angles when the hydraulic cylinder raises or lowers the rear end of the arm, thereby complicating the handling of the bridge sections.